270+ Amazing Free Java Resources To Boost Your Productivity
- Build Tool
- Bytecode Manipulation
- Cluster Management
- Code Analysis
- Constraint Satisfaction Problem Solver
- Continuous Integration
- Data structures
- Date and Time
- Dependency Injection
- Distributed Applications
- Distributed Databases
- Document Processing
- Functional Programming
- Game Development
- High Performance
- JVM and JDK
- Machine Learning
- Natural Language Processing
- REST Frameworks
- Template Engine
- Web Crawling
- Web Frameworks
Tools which handle the buildcycle of an application.
- Apache Maven - Declarative build and dependency management which favors convention over configuration. It's preferable to Apache Ant which uses a rather procedural approach and can be difficult to maintain.
- Gradle - Incremental builds which are programmed via Groovy instead of declaring XML. Works well with Maven's dependency management and treats Ant scripts as first-class citizens.
Libraries to manipulate Java bytecode programmatically.
- ASM - All purpose, low level, bytecode manipulation and analysis.
- Byte Buddy - Further simplifies bytecode generation with a fluent API.
- Javassist - Tries to simplify the editing of bytecode.
Frameworks which can dynamically manage applications inside of a cluster.
- Apache Aurora - Apache Aurora is a Mesos framework for long-running services and cron jobs.
- Singularity - Singularity is a Mesos framework that makes deployment and operations easy. It supports web services, background workers, scheduled jobs, and one-off tasks.
Tools that provide metrics and quality measurements.
- Checkstyle - Static analysis of coding conventions and standards.
- Error Prone - Catches common Java mistakes as compile-time errors.
- FindBugs - Static analysis of bytecode to find potential bugs.
- PMD - Source code analysis of bad coding practices.
- SonarQube - Integrates other analysis components via plugins and provides an overview of the metrics over time.
Frameworks that help to create parsers, interpreters or compilers.
- ANTLR - Complex full-featured framework for top-down parsing.
- JavaCC - More specific and slightly easier to learn. Has syntactic lookahead.
Libraries that provide external configuration.
- config - Configuration library for JVM languages.
Constraint Satisfaction Problem Solver
Libraries that help on implementing optimization and satisfiability problems.
- Choco - An off-the-shelf constraint satisfaction problem solver, which uses constraint programming techniques to solve constraint satisfaction problems.
- JaCoP - A constraint programming solver that includes an interface for the FlatZinc language, enabling it to execute MiniZinc models.
- OptaPlanner - A business planning and resource scheduling optimization solver.
- Sat4J - A state-of-the-art SAT solver for boolean and optimization problems in Java.
Tools which support continuously building, testing and releasing applications.
- Bamboo - Atlassian's solution with good integration of other products. You can either apply for an Open Source license or buy it.
- CircleCI - Hosted service with a free trial.
- Codeship - Hosted services with a limited free plan.
- Go - ThoughtWork's CI open source solution.
- Jenkins - Provides server-based deployment services.
- TeamCity - JetBrain's CI solution with a free version.
- Travis - Hosted service often used for open source projects.
Frameworks and libraries that simplify reading/writing CSV data.*
uniVocity-parsers - One of the fastest and most feature-complete CSV parsers for Java. Also comes with parsers for TSV and fixed width records.
Everything which simplifies interactions with the database.
- Apache Phoenix - High performance relational database layer over HBase for low latency applications.
- Flyway - Simple database migration with Java API.
- h3 - Small SQL Database notable for its in-memory functionality.
- HikariCP - High performance JDBC connection pool.
- JDBI - Convenient abstraction of JDBC.
- jOOQ - Generates typesafe code based on SQL schema.
- Liquibase - An open source database-independent library for tracking, managing and applying database schema changes.
- Presto - Distributed SQL query engine for big data.
- Querydsl - Typesafe unified queries for Java.
- Apache Parquet - A columnar storage format based on assembly algorithms from the Dremel paper by Google.
Date and Time
Libraries related to handling date and time.
- Joda-Time - De facto standard date/time-library before Java 8.
- Time4J - Advanced date and time library for Java.
Libraries that help to realize the Inversion of Control paradigm.
- Dagger - Compile-time injection framework without reflection, mainly for Android.
- Guice - Lightweight but powerful framework that completes Dagger.
- HK2 - A light-weight and dynamic dependency injection framework.
Augmentation of the development process at a fundamental level.
- ADT4J - Algebraic Data Types for Java (JSR-269 code generator).
- AspectJ - Seamless aspect-oriented programming extension.
- Auto - Collection of source code generators.
- DCEVM - Modification of the JVM that allows unlimited redefinition of loaded classes at runtime.
- Immutables - Scala-like case classes in standard Java.
- JRebel - Commercial software that instantly reloads code and configuration changes without redeploys.
- Lombok - Code-generator which aims to reduce the verbosity of Java.
- RxJava - Library for composing asynchronous and event-based programs using observable sequences from the JVM.
- Spring Loaded - Another class reloading agent for the JVM.
- vert.x - Polyglot event-driven application framework for the JVM.
Libraries and frameworks for writing distributed and fault-tolerant applications.
- Akka - Toolkit and runtime for building concurrent, distributed, and fault tolerant event-driven applications.
- Apache Storm - Distributed realtime computation system.
- Apache ZooKeeper - Coordination service with distributed configuration, synchronization, and naming registry for large distributed systems.
- Hazelcast - Distributed and highly scalable in-memory datagrid.
- Hystrix - Latency and Fault Tolerance for Distributed Systems.
- JGroups - Toolkit for reliable messaging and creating clusters whose nodes can send messages to each other.
- Orbit - Virtual Actors, adding another level of abstraction to traditional Actors.
- Quasar - Lightweight threads and actors for the JVM.
Databases in a distributed system that appear to applications as a single data source.
- Apache Cassandra - Apache Cassandra is a distributed column-oriented database providing high availability with no single point of failure.
- Apache HBase - Apache HBase is the Hadoop database, a distributed, scalable, big data store.
- Infinispan - Distributed and highly concurrent key/value datastore used for caching.
Tools which handle the distribution of Java applications in native formats.
- Bintray - Version control for binaries which handles the publishing. Can also be used with Maven or Gradle and has a free plan for Open Source Software or several business plans.
- Central Repository - Largest binary component repository available as a free service to the open source community. Default used by Apache Maven and available in all other build tools.
- IzPack - Setup authoring tool for cross-platform deployments.
- JitPack - Easy to use package repository for GitHub. Builds Maven/Gradle projects on demand and publishes ready-to-use packages.
- Launch4j - Wraps JARs in lightweight and native Windows executables.
- Nexus - Binary management with proxy and caching capabilities.
- packr - Packs your JAR, assets and JVM for native distribution on Windows, Linux and Mac OS X.
Libraries that assist with processing office document formats.
- Apache POI - Supports OOXML (XLSX, DOCX, PPTX) as well as OLE2 (XLS, DOC or PPT).
- jOpenDocument - Processes the OpenDocument format.
- documents4j - Java API for document format conversion using third-party converters such as MS Word.
Libraries that facilitate functional programming in Java.
- Functional Java - Implements numerous basic and advanced programming abstractions that assist composition oriented development.
- Javaslang - Functional component library built for Java 8+ that provides persistent data types and functional control structures.
- jOOλ - An extension to Java 8 which aims to fix gaps in lambda, providing numerous missing types and a rich set of sequential Stream API additions.
Frameworks that support the development of games.
- jMonkeyEngine - Game engine for modern 3D development.
- libGDX - All-round cross-platform, high-level framework.
- LWJGL - Robust framework that abstracts libraries like OpenGL/CL/AL.
Libraries to create modern graphical user interfaces.
Everything about high performance computation, from collections to specific libraries.
- Disruptor - Inter-thread messaging library.
- fastutil - Fast and compact type-specific collections for Java.
- GS Collections - Collection framework inspired by Smalltalk.
- Koloboke - Hash sets and hash maps.
- HPPC - Primitive collections.
- Javolution - Library for real-time and embedded systems.
- Reactor - Library for building reactive fast-data applications.
- Trove - Primitive collections.
Integrated development environments that try to simplify several aspects of development.
- Eclipse - Established, open-souce project with support for lots of plugins and languages.
- IntelliJ IDEA - Supports a lot of JVM languages and provides good options for Android development. The commercial edition targets the enterprise sector.
- NetBeans - Provides integration for several Java SE and EE features starting with database access and servers to HTML5 and AngularJS.
Libraries that assist with the creation, evaluation or manipulation of graphical images.
- Imgscalr - Imgscalr is an very simple and efficient (hardware accelerated) image-scaling library implemented in pure Java 2D.
- Picasso - Image downloading and caching library for Android.
- Thumbnailator - Thumbnailator is a high-quality thumbnail generation library for Java.
- ZXing - Multi-format 1D/2D barcode image processing library.
Libraries that simplify JSON processing.
- Genson - Powerful and easy to use Java and Scala to JSON conversion library.
- Gson - Serializes Java objects to JSON and vice versa. Good performance with on-the-fly usage.
- Jackson - Similar to GSON but has performance gains if you need to instantiate the library more often.
- LoganSquare - JSON parsing and serializing library based on Jackson's streaming API. Outpeforms GSON & Jackson's library.
JVM and JDK
Current implementations of the JVM/JDK.
Libraries that log the behavior of an application.
- Apache Log4j 2 - Complete rewrite of the previous version. Now has a powerful plugin and configuration architecture.
- kibana - Analyzes and visualizes log files.
- Logback - Founded by the same developer as Log4j and proves to be a robust logging library with interesting configuration options via Groovy.
- logstash - Tool for managing log files.
- SLF4J - Abstraction layer which is to be used with an implementation.
Tools that provide specific statistical algorithms which allow to learn from data.
- Apache Flink - Fast and reliable large-scale data processing engine.
- Apache Hadoop - Open-source software framework for storage and large-scale processing of data-sets on clusters of commodity hardware.
- Apache Mahout - Scalable algorithms focused on collaborative filtering, clustering and classification.
- Apache Spark - Open-source data analytics cluster computing framework.
- h3O - Analytics engine for statistics over big data.
- Weka - Collection of algorithms for data mining tasks ranging from pre-processing to visualization.
Tools that help sending messages between clients to ensure protocol independency.
- Aeron - Efficient reliable unicast and multicast message transport.
- Apache ActiveMQ - Open-source message broker that implements JMS and converts synchronous to asynchronous communication.
- Apache Camel - Glues together different transport APIs via Enterprise Integration Patterns.
- Apache Kafka - High-throughput distributed messaging system.
- JBoss HornetQ - Clear, concise, modular and made to be embedded.
- JeroMQ - Pure Java implementation of ZeroMQ.
- Design Patterns - Implementation and explanation of the most common design patterns.
- fabric8 - Integration platform for Java containers.
- Jimfs - In-memory file system.
- Lanterna - Easy console text GUI library similar to curses.
- LightAdmin - Pluggable CRUD UI library for rapid application development.
- Metrics - Create your own metrics or add them for supported frameworks, then expose them via JMX or HTTP, or send them to a database.
- OpenRefine - Tool for working with messy data: cleaning, transforming, extending it with web services and linking it to databases.
- RoboVM - Commercial framework with a free trial to write native iOS apps in Java.
Tools that monitor applications in production.
- AppDynamics - Commercial performance monitor.
- New Relic - Commercial performance monitor.
- Takipi - Commercial in-production error monitoring and debugging.
For working with platform-specific native libraries.
- JNA - Work with native libraries without writing JNI. Also provides interfaces to common system libraries.
Natural Language Processing
Libraries that specialize on processing text.
- Apache OpenNLP - Toolkit for common tasks like tokenization.
- CoreNLP - Stanford's CoreNLP provides a set of fundamental tools for tasks like tagging, named entity recognition, sentiment analysis and many more.
- LingPipe - Toolkit for a variety of tasks ranging from POS tagging to sentiment analysis.
- Mallet - Statistical natural language processing, document classification, clustering, topic modeling and more.
Libraries for network programming.
- Async Http Client - Asynchronous HTTP and WebSocket client library.
- Grizzly - NIO framework. Used as a network layer in Glassfish.
- Netty - A framework for building high performance network applications.
- OkHttp - An HTTP+SPDY client for Android and Java applications.
- Undertow - Web server providing both blocking and non-blocking API’s based on NIO. Used as a network layer in WildFly.
APIs which handle the persistence of objects.
- Ebean - ORM Framework that provides fast data access and even faster coding.
- EclipseLink - Supports a number of persistence standards: JPA, JAXB, JCA and SDO.
- Hibernate - Robust and widely used with an active community.
- MyBatis - Persistence framework that couples objects with stored procedures or SQL statements.
- OrmLite - Lightweight ORM package avoiding the complexity and overhead of other ORM products.
Everything that helps with the creation of PDF files.
- Apache FOP - Creates PDF from XSL-FO.
- Apache PDFBox - Toolbox for creating and manipulating PDF.
- DynamicReports - Simplifies JasperReports.
- iText - Easy to use PDF library which creates PDF files programmatically but requires a license for commercial purposes.
- JasperReports - Complex reporting engine.
Tools for performance optimization and dynamic program analysis.
- JProfiler - Commercial Java profiler.
- YourKit Java Profiler - Commercial Java profiler.
- VisualVM - Visual interface for detailed information about running applications.
Frameworks specifically for creating RESTful services.
- Dropwizard - Opinionated framework for setting up modern web applications, includes Jetty, Jackson, Jersey and Metrics.
- Feign - Java to HTTP client binder inspired by Retrofit, JAXRS-2.0, and WebSocket.
- Jersey - JAX-RS reference implementation.
- RESTEasy - Fully certified and portable implementation of the JAX-RS specification.
- RestX - Opinionated framework based one annotation processor, providing support for REST endpoint, type safe DI, hot compile/reload, API doc, metrics, specs-oriented endpoint testing.
- Retrofit - A type-safe REST client for Java.
- Spark - A Sinatra inspired framework for java.
- Swagger - Swagger is a specification and complete framework implementation for describing, producing, consuming, and visualizing RESTful web services.
Libraries for scientific computing and analysis.
- SCaVis - Environment for scientific computation, data analysis and data visualization.
Engines which index documents for search and analysis.
- Apache Solr - Full enterprise search engine optimized for high volume traffic.
- Elasticsearch - Distributed, multitenant-capable full-text search engine with a RESTful web interface and schema-free JSON documents.
Libraries that handle security, authentication, authorization or session management.
- Apache Shiro - Performs authentication, authorization, cryptography and session management.
- Cryptomator - Multiplatform transparent client-side encryption of files in the cloud.
- Keycloak - Integrated SSO and IDM for browser apps and RESTful web services. Currently in beta but looks very promising.
- PicketLink - PicketLink is an umbrella project for security and identity management for Java applications.
- Spring Security - Focuses on authentication/authorization and protects against several attack vectors.
Libraries that handle serialization with high efficiency.
- FlatBuffers - Memory efficient serialization library that can access serialized data without unpacking and parsing it.
- Kryo - Fast and efficient object graph serialization framework.
- MessagePack - Efficient binary serialization format.
Servers which are specifically used to deploy applications.
- Apache Tomcat - Robust all-round server for Servlet and JSP.
- Apache TomEE - Tomcat plus Java EE.
- GlassFish - Open source reference implementation for Java EE sponsored by Oracle.
- Jetty - Lightweight, small server, often embedded in projects.
- WebSphere Liberty - Lightweight, modular server developed by IBM
- WildFly - Formerly known as JBoss and developed by Red Hat with extensive Java EE support.
Tools which substitute expressions in a template.
- Apache Velocity - Templates for HTML pages, emails or source code generation in general.
- FreeMarker - General templating engine without any heavyweight or opinionated dependencies.
- Handlebars.java - Logic-less and semantic Mustache templates with Java.
- JavaServer Pages - Common templating for websites with custom tag libraries.
- Thymeleaf - Aims to be a substitute for JSP and works for XML files in general.
Tools that test from object to interface level including performance and other benchmarks.
- Apache JMeter - Functional testing and performance measurements.
- Arquillian - Integration and functional testing platform with integration of Java EE containers.
- AssertJ - Fluent assertions that improve readability.
- Awaitility - DSL for synchronizing asynchronous operations.
- Cucumber - A BDD testing framework that supports the most popular programming languages for the JVM.
- Gatling - Gatling is a highly capable load testing tool. It is designed for ease of use, maintainability and high performance.
- Hamcrest - Matchers that can be combined to create flexible expressions of intent.
- JMH - Microbenchmarking tool for the JVM.
- JMockit - The Mock Anything Toolkit for Java, mocks static, final methods and more.
- JUnit - Common testing framework.
- Mockito - Creation of test double objects in automated unit tests for the purpose of TDD or BDD.
- PowerMock - Allows you to unit test code normally regarded as untestable.
- Selenide - Concise API around Selenium to write stable and readable UI tests.
- Selenium - Portable software testing framework for web applications.
- Spock - Testing framework featuring an expressive Groovy-derived specification language. Compatible with JUnit runners so easy to use with standard build tools and IDEs.
- TestNG - Testing framework.
- Unitils - Testing library divided into modules for unit and integration testing.
Libraries which provide general utility functions.
- Apache Commons - Provides different general purpose functions like configuration, validation, collections, file upload or XML processing.
- args4j - Command line arguments parser.
- Guava - Collections, caching, primitives support, concurrency libraries, common annotations, string processing, I/O, and so forth.
- JADE - Providers a framework and an environment to build and to debug multi-agent systems.
- javatuples - Does what it says, although the concept of tuples in general is debatable.
- JCommander - Command line arguments parser; its been around, active, and maintained by the creator since 2010.
- JGraphT - A graph library that provides mathematical graph-theory objects and algorithms.
- JScience - Provides a set of classes to work with scientific measurements and units.
- Protégé - Provides an ontology editor and a framework to build knowledge-based systems.
Libraries that analyze the content of websites.
- Apache Nutch - Highly extensible, highly scalable Web crawler for production environment.
- Crawler4j - Simple lightweight alternative.
- JSoup - Scrapes, parses, manipulates and cleans HTML.
Frameworks that handle the communication between the layers of an web application. h
- Apache Tapestry - Component oriented framework for creating dynamic, robust, highly scalable web applications in Java.
- Apache Wicket - Component-based web application framework similar to Tapestry with a stateful GUI.
- Grails - Groovy framework with the aim to provide a highly productive environment by favoring convention over configuration, no XML and support for mixins.
- Ninja - Full stack web framework for Java. Rock solid, fast and super productive.
- Play - Uses convention over configuration, hot code reloading and display of errors in the browser.
- PrimeFaces - JSF framework which has a free and a commercial version with support. Provides several frontend components.
- Ratpack - A set of Java libraries that facilitate fast, efficient, evolvable and well tested HTTP applications.
- Spring Boot - Microframework which simplifies the development of new Spring applications.
- Spring - Aims to simplify the development with Java EE and provides packages for dependency injection and aspect-oriented programming.
- Vaadin - Event-driven framework build on top of GWT. Uses server-side architecture with Ajax on the client-side.
More Java Resources
- r/java - Subreddit for the Java community.
- stackoverflow - Question/answer platform.
- vJUG - Online Java user group.
Books about Java that had a high impact and are still worth reading.
Something to listen to while programming.
Active accounts to follow.
- Adam Bien - Freelancer: Author, JavaONE Rockstar Speaker, Consultant, Java Champion.
- Antonio Goncalves - Java Champion, JUG Leader, Devoxx France, Java EE 6/7, JCP, Author.
- Arun Gupta - Java Champion, JavaOne Rockstar, UG Leader, Devoxx4Kids-er, Red Hatter.
- Bruno Borges - Product Manager/Java Jock at Oracle.
- Ed Burns - Consulting Member of the Technical Staff at Oracle.
- Eugen Paraschiv - Author of the Spring Security Course.
- James Weaver - Java/JavaFX/IoT developer, author and speaker.
- Java EE - Official Java EE Twitter account.
- Java Magazine - Official Java Magazine account.
- Java.net - Official Java.net account.
- Java - Official Java Twitter account.
- Javin Paul - Well-known Java blogger.
- Lukas Eder - Founder and CEO Data Geekery (jOOQ).
- Mario Fusco - RedHatter, JUG coordinator, frequent speaker and author.
- Mark Reinhold - Chief Architect, Java Platform Group, Oracle.
- Markus Eisele - Java EE evangelist, Red Hat
- Martijn Verburg - London JUG co-leader, speaker, author, Java Champion and much more.
- OpenJDK - Official OpenJDK account.
- Peter Lawrey - Peter Lawrey, Java performance expert
- Reza Rahman - Java EE/GlassFish/WebLogic evangelist, author, speaker, open source hacker.
- Roberto Cortez - Java EE/JPA expert, speaker, open source
- Simon Maple - Java Champion, virtualJUG founder, LJC leader, RebelLabs author.
- Stephen Colebourne - Java Champion, speaker.
- Tim Boudreau - Author and NetBeans guru.
- Trisha Gee - Java Champion and speaker.
Sites to read.